An integrated circuit (IC) die (also called chip) is classically put into a protective package acting as a mechanical interface between said integrated circuit die and a printed circuit board (PCB). A very large number of different types of package exist, which are basically separated into two main techniques.
In the traditional wire-bond packaging technique, illustrated in FIGS. 1 and 2, an integrated circuit die 10 is placed into a protective package 12 and bond pads 9 of said integrated circuit die 10 are connected to pins 11 of said protective package 12 via tiny bond wires 13. These pins 11 are in turn connected to tracks 14 of a printed circuit board 15.
In the more recent flip-chip technique, illustrated in FIG. 3, the integrated circuit die 10 is directly connected to the printed circuit board 15 via solder balls 16 (or solder bumps). In this technique, solder balls 16 are placed onto solder pads 17 of the integrated circuit die 10. Then, the integrated circuit die 10 is flipped and placed onto the printed circuit board 15, the solder balls establishing electrical connections between the solder pads 17 and the tracks 14. As can be seen in FIG. 4, such an integrated circuit die 10 comprises an extra metal layer, called redistribution layer (RDL). The redistribution layer comprises redistribution wires 18 connecting the solder pads 17 to the input/output bond pads 14 of the integrated circuit die 10. As it is classically practiced, a bond pad 20 is dedicated to the digital ground (VSS), and another bond pad 37 is dedicated to test the die 10. Such a test is usually performed by connecting a test circuitry to the dedicated test bond pad 37 of the die 10.
There is a need to prevent a testing of the die after a flip-chip packaging operation while saving a solder ball.